Analysis of Prognostic Factors according to WHO Classification for Thymic Epithelial Tumor

Seo, Young Jun; Park, Chang Kwon; Keum, Dong Yoon; Kwon, Kun Young

Abstract

BACKGROUND
Primary thymic epithelial neoplasm is a type of mediastinal tumors that have various biologic and morphologic features. In this study, we reclassified 59 cases of thymic epithelial tumors by the new WHO classification. We inquired whether the new WHO classification has independent prognostic relevance by analyzing clinical characteristics of thymic epithelial tumors including Masaoka's clinical stage. MATERIAL AND METHOD: From December 1986 to August 2003, 59 patients who underwent surgery in the Keimyung University Dongsan Medical Center with definite diagnosis of thymic epithelial tumor were studied. We analyzed the histologic subtype (WHO classification), clinical stage (Masaoka's clinical stage) and patient's characteristics (sex, age, myasthenia gravis, tumor size, invasion, recurrence, metastasis) as prognostic factors. We analyzed the relationship between histologic subtype and clinical stage. RESULT: 32 patients were male and 27 were female. Mean age was 50.1+/-14.2. From WHO A to C, all thymic epithelial tumors were reclassified by the new WHO classification. Six patients (10.2%) had Type A, 7 (11.9%) had Type AB, 7 (11.9%) had Type B1, 10 (16.9%) had Type B2 and 7 (11.9%) had Type B3, 22 (37.3%) had Type C. Two factors were shown by multivariate analysis to be associated with a favorable prognosis: completeness of resection (p=0.003) and non-invasiveness (p=0.001). The overall 5-year survival of the 59 patients was 53%, subtype A and AB were 92.3%, B1 and B2 were 70.2%, and B3 and C were 26.1%. The association between histologic subtype and invasive behavior (stage) was statistically significant (p<0.001).
CONCLUSION
The WHO classfication is not only a histologic classfication of the thymic epithelial tumors but also a significant prognostic factor that influence the survival of thymic epithelial tumors.